NAME

gpioiic — GPIO I2C bit-banging device driver

SYNOPSIS

devicegpiodevicegpioiicdeviceiicdeviceiicbbdeviceiicbus

DESCRIPTION

The gpioiic driver provides an IIC bit-banging interface using two GPIO pins for the SCL and
SDA on the gpiobus. gpioiic implements an open colector kind of output, as recommended by
the standard, when driving the pins on the gpiobus, i.e, they are never switched to the
logical value of '1', or they are '0' or simply open (Hi-Z/tri-state). So the pullup
resistors are required so gpioiic can work.
On a hint based system, like MIPS, these values are configureable for the gpioiic:
hint.gpioiic.%d.at The gpiobus you are attaching to. Normally just gpiobus0.
hint.gpioiic.%d.pins This is a bitmask of the pins on the gpiobus that are to be used for
SCLOCK and SDATA from the GPIO IIC bit-banging bus. To configure pin
0 and 7, use the bitmask of 0b10000001 and convert it to a
hexadecimal value of 0x0081. Please note that this mask should only
ever have two bits set (any others bits - i.e., pins - will be
ignored).
hint.gpioiic.%d.scl Indicates which bit in the hint.gpioiic.%d.pins should be used as the
SCLOCK source. Optional, defaults to 0.
hint.gpioiic.%d.sda Indicates which bit in the hint.gpioiic.%d.pins should be used as the
SDATA source. Optional, defaults to 1.
On a FDT(4) based system, like ARM, the dts part for a gpioiic device usually looks like:
gpio: gpio {
gpio-controller;
...
gpioiic0 {
compatible = "gpioiic";
/*
* Attach to GPIO pins 21 and 22. Set them
* initially as inputs.
*/
gpios = <&gpio 21 1 0
&gpio 22 1 0>;
scl = <0>; /* GPIO pin 21 - optional */
sda = <1>; /* GPIO pin 22 - optional */
/* This is an example of a gpioiic child. */
gpioiic-child0 {
compatible = "lm75";
i2c-address = <0x4f>;
};
};
};
Where:
compatible Should always be set to "gpioiic".
gpios The gpios property indicates which GPIO pins should be used for SCLOCK and SDATA
on the GPIO IIC bit-banging bus. For more details about the gpios property,
please consult /usr/src/sys/boot/fdt/dts/bindings-gpio.txt.
scl The scl option indicates which bit in the gpios should be used as the SCLOCK
source. Optional, defaults to 0.
sda The sda option indicates which bit in the gpios should be used as the SDATA
source. Optional, defaults to 1.